You may think, salt is just a simple cooking element we shake on our food for a little extra taste. But salt is much more than that. Without salt our muscles would not move. Our nervous systems would not operate. Our hearts would not beat.

　　But do not think rubbing salt in a wound will help. Doing that would be painful and not heal the wound. To rub salt in a wound is an idiom that means to purposefully make a bad situation worse.

　　Early humans got the salt they needed to stay alive from the animals they killed. But advances in agriculture led to a diet low in salt. So, humans needed to find other sources. Those who lived near the ocean or other natural sources for salt were lucky. Those who did not had to trade for salt. In fact, people used salt as a method of payment in many parts of the ancient world. The word "salary" comes from the word "salt". Salt also played an important part in population movement and world exploration. Explorers understood that if they could keep food fresh, they could travel longer distances. So they used salt to preserve food and explored the world.

　　Salt was so important that, according to food historians, it was traded pound-for- pound for gold. Today, people still use the expressions "to be worth one's salt" or "worth one's weight in salt". The expressions describe a person of value. A person might also be called "salt of the earth". That description means he or she is dependable and trustworthy. However, when you say "I think we should take what he said with a grain of salt" you mean you accept it but maintain a degree of doubt about its truth.

28. What is the main idea of the first paragraph?

A. Salt plays an important part in our life.

B. Salt makes food tasty.

C. Salt is considered to be part of our muscles.

D. Salt is simple as a seasoning (调料).

29. If a beggar's bread is stolen, we can describe the matter as ______.

A. salt of the earth B. to be worth his salt